Posterior

The posterior, individually buttocks, colloquially referred to as one's bum, butt, booty or arse, was the backside of humanoid life forms, and many other bipeds or quadrupeds. As well as depositing bodily wastes and gasses, the buttocks were also a common focal point of sexuality.

The phrase "kicking butt" was used in slang to describe besting an adversary. After successfully evading the surveillance of the Department with K9 Mark 2, Starkey announced that they had "kicked surveillance butt". In response, his robotic friend vowed to "kick surveillance posterior" whenever possible from then on. (TV: The Korven)

Words relating to the posterior were also used as insults. The Testimony glass avatar version of Bill Potts angrily called the Twelfth Doctor a "stupid bloody arse" for not believing she was the real Bill. (TV: Twice Upon a Time)